Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing my new design;

FIG. 2 is the second image thereof; and,

FIG. 3 is the third image thereof.

The broken lines illustrate the display screen or portion thereof and form no part of the claimed design. The broken lines illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described herein. 